Physiological Responses of Field Grown Lemongrass (Cymbopogon citratus) to Seasonal Changes

Abstract

A population of lemongrass (Cymbopogon citratus) was investigated in this research for changes in metabolite profiles in the leaves of different ages i.e. penultimate (second fully expanded leaf from the top), middle (a leaf from the central position of a tiller) and bottom (a lowermost green leaf on a tiller) with changing seasons round the year for two consecutive years (2010-2011). Measurements were made for some primary and secondary metabolites while the essential oils profile of leaves was analyzed using GC-MS. The photosynthetic pigments displayed sharp variations in the leaves of different ages with changes in the environmental conditions. Higher chlorophyll a, b and carotenoid were recorded during summer months. The accumulation trends of osmolytes in lemongrass showed notable seasonal variation. The accumulation of total free amino acids, free proline and GB were higher during summer months. The antioxidant enzymes minimized the effect of oxidative damage by scavenging H 2 O 2 and reuced MDA contents in extreme environmental conditions especially during summer. The younger leaves of lemongrass exhibited much higher concentrations of vitamins as compared to bottom leaves. The secondary metabolites i.e. alkaloid, phenolic and flavonoid contents in lemongrass leaves were markedly increased with increased temperature. Seasonal variation affected the nutritional profile of lemongrass substantially. The production of NDF ADF, ADL, cellulose and starch was greater during summer. Cellulose and silica contents were higher in bottom leaf possibly due to plant aging. Starch content was higher in penultimate leaf, which declined with leaf age. Mineral concentration of lemongrass appears to be largely dependent on temperature and evapotranspiration. The GC-MS analysis of lemongrass oil carried out in the leaf samples collected during January, April, July and October revealed that out of 54 compounds analyzed, neral, citral, geranial, allerthin, caryophyllene oxide were major ones synthesized in various sesasons.